I think the example I gave above, along with the questions it raises about the "evidence" against me, would be easy enough for any non-technical minded jury to grasp. Those questions, really make it clear that anybody could've done it. Basically, if there's just 3 people who had access to my internet account, then the likelyhood of any single individual being the one who did it, is only 33%, not 100% or even 50%. Therefore, it's more unlikely that said individual downloaded the copyrighted material, than it is likely they did it.
By the time the prosecution gets a search warrant to comb through all the files on all the devices, the downloaded copyrighted material could have been moved to another device or hard drive. If they finds signs that it existed on one of the devices & no longer exists, the defendant can claim they downloaded the file but it wasn't what they wanted or that they decided not to keep it, so they deleted it. That wouldn't be much different than buying something from Walmart & returning it to get your money back. Even better, it's like a thief who walks out of a store with something, but then returns it to the shelf before anyone busts him. Even if he's noticed on security camera's after the fact, they can't legally make you pay for something you're not keeping or using.
So the case against an individual is so weak that even preponderance isn't really a problem. In fact, it just wouldn't be worth the money it costs to try to fight it in court. For argument's sake though, imagine Rightscorp & the ISP's did allow cases like these to be brought to court and they win a lot of them. The moment ONE of them ends with the defendant being innocent, it creates a precedent. That'd be their worst nightmare, and they do NOT want to risk that happening. The gig would be up, forever.